Explosion at a hydrocracking reactor of a refinery

Event

Event ID: 614
Quality: 2
Description: An explosion occurred in a hydrocracking reactor fitted with TOC which is a automatic cut-off system for raw oil and hydrogen supply. On the day of the incident, the operation was stopped because the TOC activated, but the cause was not identified. Hydrogen circulation was restarted, and some 5 hours later, the loud explosion took place around a low pressure separator, rupturing the reactor and throwing debris in all directions. The contents were released to form a vapour cloud which ignited followed by a fire ball.
Event Initiating system: Hydrogen system initiating event
Classification of the physical effects: Hydrogen Release and Ignition
Nature of the consequences: explosion
Macro-region: Asia
Country: Japan
Date: 01/01/1987
Component involved: off-gas system
Failure mode: internal explosion
Initiating cause: unknown
Root causes: Unknown
Date entry in HIAD: 01/01/2020

Application: Petrochemical industry
Sub-application: Hydrocracking process
Hydrogen supply chain stage: Hydrogen as process gas
All components affected: oil and raw supply, low pressure separator, reactor
Process temperature range [C]: Very high temperature (500°C to 1000°C)
Process pressure range [MPa]: medium to high pressure (10 to 50 MPa)
Location type: Unknown
Location: industrial area
Operational condition: ABNORMAL
Pre-event occurrences: The pre-event related to the hydrogen-event was an automatic stop of the unit, before the hydrogen was recirculated.
Description of the facility/unit/process/substances: A TOC is an automatic cut-off system for the supply of raw oil (feedstock) and hydrogen. It is designed to stop the flow of highly flammable materials into the hydrocracking reactor in an emergency, such as a fire or explosion, to prevent the incident from escalating.